Authenticate finds a user by their email and verifies their password.

Create inserts a new user into the database.

Delete removes a user from the database.

List retrieves a list of existing users from the database.

Retrieve gets the specified user from the database.

Update replaces a user document in the database.

ErrAuthenticationFailure occurs when a user attempts to authenticate but anything goes wrong.

ErrInvalidID occurs when an ID is not in a valid form.

ErrNotFound abstracts the postgres not found error.

ErrValidateConfirmPassword occurs when password doesn't match.

NewUser contains information needed to create a new User.

UpdateUser defines what information may be provided to modify an existing User.

User represents user in database.